This invention relates to an improved heat exchange tubing assembly and to an improved method for fabricating a heat exchange tubing assembly.
Various forms of heat exchange apparatus such as heating and air conditioning apparatus, include a heat exchange tube assembly through which is conveyed a heating or cooling medium. An exchange of thermal energy occurs between this medium and a second medium flowing over the tubing. Heat exchange with the second medium is enhanced by provided a plurality of heat exchange blades which are maintained in thermal contact with the tubing. The blades have a surface area substantially greater than their thickness and increase the effective heat transfer surface which is exposed to the surrounding atmosphere. One such arrangement is described in U.S. Pat. No. 3,457,756, wherein the tube includes integral flat flange segments and the blades are integrally formed with the tube from the flange segments. In another arrangement, the blades are integrally formed in a strip of material which is then continuously helically wound on the tube and secured thereto by an adhesive which is positioned between the strip and the tube.
These prior techniques for increasing the effective heat transfer surface exhibit several disadvantages. When the blades are integrally formed with the tubulation, the number of blades which can be provided to increase the heat transfer surface is substantially limit since a tabulation can provide only a limited number of flat flanges before the cost and assembly procedures become uneconomical and cumbersome. When the blades are formed in a strip which is wound about the tubulation, it has been found that the adhesive used for bonding limits the thermal-conductivity between the blades and the tubulation. In some cases, additional metal, with concomitant additional weight and cost, may be used in the tubing or in the bladed strip or in both to compensate for the thermal insulation effect of the non-metallic bonding layer between the tubing and bladed strip. In addition, fabrication of the heat exchange assembly by helically winding the strip on the tubing is relatively slow and reduces the production capability while increasing the overall cost of the heat exchange tubing assembly.
Furthermore, with the helically wound bladed strip the individual blades become generally uniformly distributed around the full periphery of the circular tubing. When the external fluid medium flows past this bladed tubing in a direction generally perpendicular to the tubing axis, there are fluid flow "dead spaces" which occur immediately ahead of and immediately behind the tubing. The particular blades which happen to project forward ahead of the tubing or backward behind the tubing are resident in these dead space regions where the fluid flow is slow or stagnant. Accordingly, such blades are not very effective in contributing to the overall heat exchange capacity of any apparatus in which such prior art tubing is utilized.
Accordingly, it is an object of this invention to provide an improved heat exchange tube assembly.
Another object of the invention is to provide an improved method for fabricating a heat exchange assembly.
Another object of the invention is to provide a heat exchange tube assembly having improved means of mounting a blade strip to the tubulation.
It is a further object of the present invention in accordance with a presently preferred embodiment thereof to provide a streamlined tube assembly which reduces the dead spaces ahead of and behind the tubing and wherein the blades fan out into regions on opposite sides of the tubing where the external fluid flow is relatively unimpeded by the streamlined tubing itself.